Crop shear knife and method of operating same

ABSTRACT

The forward-facing shearing knife of a pair of crop shear knives mounted on adjacent rotatable heads has its shearing face so inclined that when reaching the initial position at which penetration of the work commences, it is approximately perpendicular to the plane of the work, and during the shearing operation it extends angularly away from and rearwardly at an increasing angle with respect to the plane and direction of movement of the stock. The work-engaging end surface of the knife is inclined inwardly and rearwardly with respect to a plane tangent to the shearing edge. The inclination of these two surfaces is such that during engagement with the work the nonradial force vectors on the knife and drum are substantially eliminated, thereby eliminating damaging stresses and improving the shearing of heavy stock such as hot rolled steel plate.

O United States Patent 13,570,363

[72] Inventor Wilbur C. Thomas 2,233,922 3/1941 Kaddeland 83/342X 8Clinton Lane, Dear-born, Mich. 48120 2,246,957 6/1941 Shields 83/341[21] Appl. No. 882,761 2,768,690 10/1956 Roberts et a1.. 83/345X [22]Filed Dec. 17, 1969 3,084,582 4/1963 Anderson 83/341 [45] Patented g f iga zzh pp Ser No Primary Examiner-James M. Meister 681,850 Nov. 9, 1967Attorney-Harness, Dickey & Pierce [54] CROP SHEAR KNIFE AND METHOD OFABSTRACT: The forward-facing shearing knife of a pair of OPERATING SAMEcrop shear knives mounted on ad acent rotatable heads has its 8 Claims,6 Drawing Figs shearing face so inclined that when reaching theinitialpositlon at whlch penetration of the work commences, 1t is ap-U.S. proximately perpendicular to the plane of the work, and dur-83/341, 83/345, 83/673 ing the shearing operation it extends angularlyaway from and [51] Int. Cl. B23d 25/12 rearwardly at an increasing anglewith respect to h plane and Fleld ofsealch direction of movement of thetock The work engaging end 674 surface of the knife is inclined inwardlyand rearwardly with respect to a plane tangent to the shearing edge. Theinclina- [56] References cued tion of these two surfaces is such thatduring engagement with UNITED STATES PATENTS the work the nonradialforce vectors on the knife and drum 971,022 9/ 1910 Cooper 83/341X aresubstantially eliminated, thereby eliminating damaging 2,020,996 11/1935Crafts 83/342X stresses and improving the shearing of heavy stock suchas hot 2,052,461 8/ 1936 Greenwood 83/341X rolled steel plate.

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5 Sheets-Sheet 5 INVENTOR.

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CROP SHEAR KNIFE AND METHOD OF OPERATHQG SAME The present application isa continuation of my previously filed copending application Ser. No.681,850, filed Nov. 9, i967, now abandoned.

BACKGROUND OF THE INVENTION Rotatable-head-type shearing units for hotrolled steel plate stock have been employed heretofore which may be upto 4 feet in diameter or even larger. The heads may be 6 or more feet inlength requiring knives of substantially the same length. Usually, oneor a plurality of sets. of knives are employed on the heads and pairs ofthe knives engage the plate on opposite sides as it is advanced betweenthe rollers, shearing being completed substantially as the cutting edgesreach the vertical plane through the axes of the heads. The knives maybe straight or may be slightly arced end to end so as to have thecenters of the sheared edges disposed forwardly of the ends of suchedges. Arcuate contouring facilitates entry of the central portion ofthe forward edge of the cropped plate into the rolls of a rolling mill,when the plate is fed therethrough to have its thickness reduced. Suchknives as heretofore constructed and operated were of likecross-sectional form and the forwardly directed shearing face of oneknife was disposed at the same angle to the axis of rotation as therearwardly directed shearing face of the mating knife, these shearingfaces normally being radial. Substantial noise, vibration and wear onthe driving gears occurred, and the life of such equipment wasrelatively short, for reasons not previously understood.

As a result of the undesirable vectors of the heavy forces exertedduring the shearing operation, the gears for driving the rolls quicklybecame worn, requiring early replacement. In studying the operation, itwas found that the shape of the knife having the forwardly directedcutting edge is critical, and that when such knives are constructed andoperated in accordance with prior practice, the force vectors are suchthat heavy components are directed nonradially, stressing the gears anddrive train beyond desirable limits, and, further, that such knife alsoincorporates areas which actually interfere with the displacement of apart of the metal, rendering it extremely difficult to reliably produceclean, high-quality cuts of heavy hot-rolled plate on such machines,without frequent costly shutdown of the shear for repairs.

By redesigning the contour of the knife which carries the forwardlydirected shearing face, following an improved method of disposing itsworking surfaces in accordance with criteria derived from the orbitradius and the thickness of the work, I have succeeded in greatlyreducing shock, noise and vibration, eliminating excessive wear of thedriving gears and improving the quality of cut and the life of theknives and other parts. The accomplishment of these improvementsconstitutes the overall objective of the present invention.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is 'a somewhat diagrammaticcross-sectional view of the rotatable heads of a rotary shear having twosets of crop shear knives thereon with one set of knives shown in theposition they occupy at the completion of a shear;

FIG. 2 is an enlarged broken and somewhat diagrammatic sectional view ofthe structure illustrated in FIG. 1, as viewed within the oval 2thereof;

F IG. 3 is a diagrammatic view showing the knives at successiveoperative positions with respect to the work and illustrating thetriangulation needed to determine the contouring of the trailing knifein accordance with a preferred practice of my invention;

FIG. 4: is a free body diagram indicating the forces in the work andblades during a shearing operation performed in accordance with myinvention;

FIG. 3 is a diagrammatic view illustrating three positions showingconventional knives in successive operative positions during theperformance of an analogous shearing operation utilizing the prior artapparatus and under typical conditions which exist after wear hasoccurred in the driving gears of the shear, the related drive gear toothrelationship also being diagrammatically indicated; and

FIG. 6 is a force diagram similar to FIG. 4 but showing the forces inthe work and blades during a shearing operation performed by aconventional prior art construction such as is illustrated in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows in cross sectionthe rotary heads of a crop shear such as is used for cutting heavyhot-rolled steel plate, the heads being of conventional construction butthe knives being of an improved type incorporating my present invention.

The heads 11 and 12 are synchronously driven in rotation in oppositeangular directions. In the FIGS. the head 11 is rotated counterclockwiseabout axis X, while the head 12 is rotated clockwise about axis Y. Theforward edge of the work 13 is cropped by a pair of knives 15 and 16which have the shearing edgesarced from end to end to cut a convex endon the forward end of the plate. Shims 20 and clamping mechanisms 17retain the blades in fixed position on the heads with the are alongwhich the cut is made falling equal amounts on opposite sides of thecenter rotation of the heads. The plate 13 is fed to a positioncentrally between the knives 15 and 16 sufficiently to permit theforward material to be sheared from the plate on the arc of the shearingedges. These features of mounting and curvature are known in the art,the symmetrical forward curvature and resultant convexity of the leadingedge of the severed work being provided in order to assist the work tofeed into the rolls of a mill. Wording employed in the specification andclaims of the present application which refers to the knives of theircutting edges as extending generally parallel or substantially parallelto the axis of rotation is therefore intended to encompass both astraight edge paralleled to the axis of rotation, and an edge whichdiverges symmetrically away from such a straight line from a pointmidway of its length toward its two ends; as distinguished, for example,from a helical or unsymmetrical edge. The knives l5 and 16 initiallywill be located approximately 30 above and below the horizontal linebetween the heads indicated by the dot-dash line 18, whereupon the twoheads 11 and 12 will be rotated in synchronous relation to have theknives move toward the plate until the plate is engaged thereby, at aposition of initial effective contact just prior to penetration andcorresponding to positionl, FIG. 3, whereafter continued rotation of theheads to the position of maximum penetration shown at III causessevering of the stock, which occurs substantially prior to attainment ofposition III, with hot-rolled steel plate. Because such work seversbefore the cutting edges of the two knives reach the pass line, it isthe present practice in the art to provide no overlap of the knives atfull penetration, or only a very slight overlap, as shown. This avoidsthe necessity of providing any relief angle or back draft on crop shearknives employed to sever heavy and resistant stock such as steel platehaving thicknesses of one-half inch and greater. If such relief angleswere employed in the ways employed on many tools and cutters intendedfor other types of work, weakening of the tool would result, and suchrelief angles have therefore been avoided in the type of service underconsideration.

The direction of feed is denotedby arrow A. Heretofore, the two kniveshave in usual trade practice had the same crosssectional contour, withshear faces approximately radial, and perpendicular to the plane of thework when the cutting edges have reached the full-in position, as shownin FIGS. 5 and 6.

The outer surface 26 of the knife has in some instances in the past beentangent to the orbit of the cutting edge, or approximately perpendicularto the shearing face, rather than inclined inwardly as shown. In otherinstances it has been inclined at a small angle with no criterionalbasis. In a preferred design constructed in accordance with thisinvention, surface 26 is inclined inwardly from the cutting edge 19 atan angle of approximately 12 to a tangent plane.

The plate is to be sheared along a line 22 and the leading blade 15 isurging the forward part 23 of the plate downwardly while the trailingblade 16 is urging the rearward part 24 of the plate upwardly as theknives move toward the right from the dot-dash position to the full lineposition shown in FIG. 2. If the trailing knife 16 were of the samecontour as the leading knife 15, in accordance with current practice(see blade 16A, FIG. its shearing face 25A would, at the position ofinitial operative contact, be as indicated in dotted lines at 25A inFIG. 2, and in full lines at position I in FIG. 5, that is, at an angleof substantially less than 90 to the plane of the work. Under suchusually employed conditions, the prior art type of trailing knife,during its forward travel from the position of initial operativeengagement (position I, FIG. 5) during its penetration of the workupsets metal forwardly of the intended shear line 22, thereby not onlyresisting the downward movement of the forward portion 23 of the workbut due to its angularity also creating a large reactive tangentialcomponent (-FS, FIG. 6) rearwardly and which is substantiallycounterclockwise, as well as a radial inward force reaction (-F6) whichalso has a counterclockwise component. These components impose a heavyrearward load on the knife 16A, and thereby on the gear 41 which drivesthe trailing knife head. Such action absorbs much energy, produces heavypounding noise and vibration, and causes rapid wear of the drivinggears.

In FIG. 5 three operative positions of such conventional prior artknives are shown typifying relative positionings they assume after thedriving gears have become worn. As shown in position I, representing thepoint at which initial engagement occurs, the cutting edges of theknives initially engage the work in proper registry with the desiredshear line 22. Such proper engagement occurs even if the gears havebecome worn, because those teeth which are effective to move the knivesthrough that portion of their travel which occurs prior to workengagement are substantially unloaded and therefore do not suffermaterial wear during use. As the knives penetrate the work, however, theforce vectors shown in FIG. 6 develop, and the reactive forces -F6 and-F5 impose a severe rearward load in the manner previously described.The driving gear 42 for the leading knife rotor is subjected to a heavyopposed loading due to the force transmitted through the work. Thoseteeth of both gears which are in driving engagement during the shearingoperation are accordingly subjected to heavy loading which rapidly wearstheir driving surfaces in the working areas. An excessive clearancetherefore unavoidably develops between such teeth, as is represented inFIG. 5 by the gap 44. At position II the leading knife A is shownperpendicular to the plane of the work, corresponding to the position ofmaximum penetration of the leading knife. As also shown at position II,however, the trailing knife 16A, due to the wear corresponding to thegap 44, does not reach the intended position of approximateperpendicularity and close abutting relationship to the knife 15A (as itdoes prior to wear of the gears) and accordingly knife 16A trails theknife 15A to an exaggerated degree, leaving an unsevered neck 45 in thework between the main mass 24- and the portion 23 which should becropped (but which under such conditions may not be severed from themain mass at all, depending upon the amount of wear which has occurredand the nature of the work). It will also be seen that during such anoperation the end surface of the leading knife 15A drives section 23downwardly over the front face of the trailing knife 16A, and that ifthe work remains unsevered at the neck 45, the trailing knife furtherdistorts the work, driving the front section 23 back upwardly as thework and knives continue toward position III. Severe wiping engagementsthus occur between the cutting edges and surfaces ofthe knives and thework. This not only imposes severe loads but dulls the edges.

To alleviate this situation, I form the shearing face 25 of the trailingknife 16 at an angle such that it inclines rearwardly and inwardly fromits leading work engaging edge 19 to a degree such that it extendssubstantially perpendicularly to the face of the work when it firstoperatively engages the bottom surface thereof. It will be seen that theangle of inclination at the position of initial engagement could begreater than but that the knife is weakened as this angle is increased.I therefore preferably form the shearing surface at an angle whichintersects the shearing edge and which is so related to the radius oftheorbit of such edge, and to the thickness of the work, that shearingsurface 25 is perpendicular to the plane of the work at the position ofinitial penetration, and increases as shearing proceeds. The inclinationof outer or end surface 26 is also selected so that no material rubbingoccurs, and to create a forward force vector on the trailing knife.

Referring to position I of FIG. 3 showing a preferred form of myimproved construction more particularly, it will be noted that thecutting edge 25 of the trailing knife is defined by a front surfacewhich is inclined to the radial plane at an angle which slightly exceeds(e.g: by '2?) the minimum angle required in order to position suchleading surface perpendicularly with respect to the plane of the work.Such slightly excess angularity or relief insures total elimination ofvectors corresponding to F5 and F6, referred to above. It will be notedfrom the successive positions in FIG. 3 that the shearing action is freeto occur along the shear line 22 without creating any angular componentsother than those shown in FIG. 4.

The actual values of the remaining forces which occur in the knives andwork when my invention is used will of course depend not only upon theangularity of the end face 26 but also on the plastic flow properties ofthe work being cut. The vector arrows in FIG. 4 (and also in FIG. 6) areof course only illustrative, and it will be understood that they varyduring operation, but the loads on the knives and drive mechanism aregreatly reduced in any event, and the lives of the knives and drivinggears are greatly lengthened. The initially set relationship between theknives for proper shearing is maintained for a much longer period oftime than has heretofore been possible. As also shown in FIG. 3, theangular section 25 which constitutes the shearing face of the trailingknife extends radially inwardly a distance at least equal to one-halfthe work thickness plus the knife overlap, and preferably also includingat least a slight clearance. For maximum blade strength, however, theinclined shearing face need not extend inwardly farther than is requiredto provide adequate work clearance. In practice, in sharpening myimproved trailing knives, I leave a radial land (19, FIG. 4) at theshearing edge 19 which is not over .060 inches wide. With hot-rolledsteel stock sheared by my improved knives a land of this width has beenfound not to create undue stresses, due, presumably, to the fact thatthe distorting effect on the land does not stress the work beyond itselastic limit. If the land becomes too wide, however, the effect issimilar to a full radial face such as has been employed on prior artknives. The complete shearing occurs when the shearing edges of theknives are substantially in a vertical plane through the axes of theheads, as illustrated in FIG. 2. FIGS. 1 and 2 show curved knives, asnoted above, whereas no curvature is indicated in FIGS. 3-6. Both typesof knives are commonly used in the trade, and the operating principlesare the same, insofar as my invention is concerned.

In such shears the pass line A is tangent to the pitch circle of thegears. The minimum angle which shearing face 25 should make to theradius is derivable from the cosine of the angle between the adjacentside of the hypotenuse of a right triangle whose adjacent side is aradius perpendicular to the pass line and terminating at the closestsurface of the work and whose hypotenuse is the radial distance from theaxis to the shearing edge, which corresponds to a radius to the positionof initial contact. The adjacent side defined by a line which is theshortest (perpendicular) radius to the bottom or nearer plane of thework is equal to PR/2W. The hypotenuse which is the radial line to thepoint of initial contact, is equal to PR+L,

decelerating heads continue to rotate beyond the shear point to permitthe automatic reverse rotation of the heads to their starting positionswhich is that wherein the knives are located substantially on the lines18.

Cropping of the rear end of the plate may be performed by knives 27 and28 disposed diametrically opposite to the knives ifs-and l6, and shownas straight rather than curved. These knives are located on the lines 18before the shearing operation and the plate 113 is advanced between theheads 11 and 12 until the rear end to be cropped is'located in aposition to be engaged by the shearing edges of the knives 27 and 28 asthey are advanced. It will be noted in this arrangement that knife 28 issimilar to knife 16 in cross section, its shearing face 29 beingsimilarly inclined in an amount such that when in engagement with thework the-included angle between its shearing face and the surface of thework is at all times substantially equal to or greater than 90, as inthe case of the shearing face 25 of knife 16, and its outerwork-engaging surface 36 is inclined similarly to surface 26.

It has been found upon employing crop-knives contoured in the disclosedmanner that the heavy noise occurring from initial contact issubstantially reduced, the cutting life of the shearing edges issubstantially increased, and the excessive wear of the driving gearscompletely eliminated.

This detailed description of preferred form of the invention, and theaccompanying drawings, have been furnished in compliance with thestatutory requirement to set forth thebest mode contemplated by theinventor of carrying out the invention. The prior portions consisting ofthe Abstract of the Disclosure and the Background of the Invention arefurnished without prejudice in an effort to comply with administrativerequirements of the Patent Office' l claim:

1. ln crop shear apparatus for severing relatively thick and resistantstock, said apparatus'comprising a pair of knife supports arranged torotate synchronously in opposite angular directions around parallelaxes, a pair of knives one of which is carried by each of said supportsand each of which knives has an outer cutting edge extendinglongitudinally generally parallel to the axis of rotation of itssupport, said knives being rotatable in circular orbits of like radiusinto and out of a cutting edge-abutting position which corresponds tomaximum stock penetration without substantial overlap of the knives, thenovelty which comprises a trailing knife having a forwardly directedshearing face extending inwardly from said cutting edge and inclinedrearwardly with respect to a radius at an angle which is so related tothe radius and to the thickness of the work that the included forwardangle between said shearing face and the work at the position of initialeffective contact with the work just prior to penetration issubstantially 90 and increases during continued rotation, and a leadingknife having a rearwardly directed shearing face extending inwardly fromits cutting edge at an included rearward angle which decreases duringcontinued rotation and which, at said position of initial contact, isnot less than 90 to the plane of the work and not greater than the anglebetween the plane of the work and a radial line projected from thecuttingedge to the axis of rotation.

2. Crop shear apparatus as defined in claim 1 wherein said trailingknife has an outer surface extending rearwardly away from said cuttingedge and shearing face and diverging from the plane of the work at anangle sufficient to create a forward component of force on the knife asit enetrates the work.

. Crop shear apparatus as define in claim 1 wherein said included anglebetween the shearing face of the trailing knife and the stock at saidposition of initial contact is slightly greater than 90.

4. Crop shear apparatus as defined in claim 1 including a narrow radialland between the cutting edge and the shearing face of said trailingknife.

5. Crop shear apparatus as defined in claim 1 including a narrow radialland of a width-not exceeding .060 inch between the cutting edge and theshearing face of said trailing knife.

6. The method of shearing plate stock in a crop shear which comprisesdetermining the radius of the orbits of the knives and the thickness ofthe work, arranging the forwardly facing shearing face of the trailingknife to substantially intersect the shearing edge and at an angle suchthat at its position of initial operative engagement with the work theincluded angle between the shearing face and the plane of the work isequal to or greater than 90, arranging the rearwardly facing shearingface of the leading knife to extend inwardly from its shearing edge atan included angle to the work which at said position is not less than 90to the plane of the work and not greater than the angle between theplane of the work and a radial line projected from the cutting edge tothe axis of rotation, and rotating the knives synchronously in oppositeangular directions around parallel axes to bring their shearing edgesinto edge abutting position without substantial overlap and shearing thework while increasing the first-mentioned included angle and decreasingthe second-mentioned included angle.

7. The method defined in claim 6 wherein said first-mentioned knife isurged forwardly in its orbit by reaction of the work against an inclinedouter surface of the knife.

8. The method of severing heavy metal plate stock or the like with arotary shear of the type having paired leading and trailing shearingknives orbitally synchronously rotatable in opposite angular directionsabout parallel axes toward and from a closely adjacent position at aninterposed pass line while the stock is moving therebetween along thepass line which comprises determining the length of a straight line fromthe axis of rotation of the trailing knife to the nearest point on thesurface of the stock, determining the length of a radial line from saidaxis to the pass line, determining the angle corresponding to the cosineof the angle between said lines when a right triangle is constructedtherefrom having its hypotenuse corresponding to said radial line andits third side corresponding to a line on the surface of the stockclosest to the trailing knife, arranging a forwardly facing shearingsurface on the trailing knife at such an angle to a radial lineprojected to its shearing edge that said shearing surface slopesrearwardly and inwardly with respect to said last-mentioned radial lineat an angle which is not materially less than the angle corresponding tosuch cosine, and shearing the stock in the shear between said knives.

1. In crop shear apparatus for severing relatively thick and resistantstock, said apparatus comprising a pair of knife supports arranged torotate synchronously in opposite angular directions around parallelaxes, a pair of knives one of which is carried by each of said supportsand each of which knives has an outer cutting edge extendinglongitudinally generally parallel to the axis of rotation of itssupport, said knives being rotatable in circular orbits of like radiusinto and out of a cutting edgeabutting position which corresponds tomaximum stock penetration without substantial overlap of the knives, thenovelty which comprises a trailing knife having a forwardly directedshearing face extending inwardly from said cutting edge and inclinedrearwardly with respect to a radius at an angle which is so related tothe radius and to the thickness of the work that the included forwardangle between said shearing face and the work at the position of initialeffective contact with the work just prior to penetration issubstantially 90* and increases during continued rotation, and a leadingknife having a rearwardly directed shearing face extending inwardly fromits cutting edge at an included rearward angle which decreases duringcontinued rotation and which, at said position of initial contact, isnot less than 90* to the plane of the work and not greater than theangle between the plane of the work and a radial line projected from thecutting edge to the axis of rotation.
 2. Crop shear apparatus as definedin claim 1 wherein said trailing knife has an outer surface extendingrearwardly away from said cutting edge and shearing face and divergingfrom the plane of the work at an angle sufficient to create a forwardcomponent of force on the knife as it penetrates the work.
 3. Crop shearapparatus as defined in claim 1 wherein said included angle between theshearing face of the trailing knife and the stock at said position ofinitial contact is slightly greater than 90*.
 4. Crop shear apparatus asdefined in claim 1 including a narrow radial land between the cuttingedge and the shearing face of said trailing knife.
 5. Crop shearapparatus as defined in claim 1 including a narrow radial land of awidth not exceeding .060 inch between the cutting edge and the shearingface of said trailing knife.
 6. The method of shearing plate stock in acrop shear which comprises determining the radius of the orbits of theknives and the thickness of the work, arranging the forwardly facingshearing face of the trailing knife to substantially intersect theshearing edge and at an angle such that at its position of initialoperative engagement with the work the included angle between theshearing face and the plane of the work is equal to or greater than 90*,arranging the rearwardly facing shearing face of the leading knife toextend inwardly from its shearing edge at an included angle to the workwhich at said position is not less than 90* to the plane of the work andnot greater than the angle between the plane of the work and a radialline projected from the cutting edge to the axis of rotation, androtating the knives synchronously in opposite angular directions aroundparallel axes to bring their shearing edges into edge abutting positionwithout substantial overlap and shearing the work while increasing thefirst-mentioned included angle and decreasing the second-mentionedincluded angle.
 7. The method defined in claim 6 wherein saidfirst-mentioned knife is urged forwardly in its orbit by reaction of thework against an inclined outer surface of the knife.
 8. The method ofsevering heavy metal plate stock or the like with a rotary shear of thetype having paired leading and trailing shearing knives orbitallysynchronously rotatable in opposite angular directions about parallelaxes toward and from a closely adjacent position at an interposed passline while the stock is moving therebetween along the pass line whichcomprises determining the length of a straight line from the axis ofrotation of the trailing knife to the nearest point on the surface ofthe stock, determining the length of a radial line from said axis to thepass line, determining the angle corresponding to the cosine of theangle between said lines when a right triangle is constructed therefromhaving its hypotenuse corresponding to said radial line and its thirdside corresponding to a line on the surface of the stock closest to thetrailing knife, arranging a forwardly facing shearing surface on thetrailing knife at such an angle to a radial line projected to itsshearing edge that said shearing surface slopes rearwardly and inwardlywith respect to said last-mentioned radial line at an angle which is notmaterially less than the angle corresponding to such cosine, andshearing the stock in the shear between said knives.